You may encounter this error when you're trying to disable or delete a custom field.
When setting up single sign-on (SSO) for Directory apps and non-Directory SAML apps, a value called
Name ID
can be passed from Zoho Directory to the application. The application will use this Name ID to identify the user trying to sign in. This value will usually be the Primary Email Address. But you can also pass any user information field in Zoho One as the Name ID.
Learn more about setting Name IDs
If the Name ID is not passed to an app, SSO for the app might fail. So you will not be allowed to disable or delete a custom field if the custom field is set as the Name ID of a Directory or a non-Directory app.